Compared with the extrusion molding, in which the deformation force acts simultaneously on the entire workpiece surface, in the case of wobble-die forging, force is as known exerted only on a partial surface, whereby only small friction can arise and the material flows in radial direction without great resistance. For this, the blank is deformed between an upper die and a lower die with a circularly rocking movement of the upper die, so that the effective deformation force is concentrated on only a partial surface of the work-piece. The deformation is effected by movement of the pressure zone over the entire workpiece surface.
Due to the smaller contact area and the more favorable friction conditions, the deformation force in wobble-die forging machines is thus substantially smaller than in the case of conventional extrusion molding.
Resulting from this are the advantages of appreciably smaller machines, smaller die loading and smaller noise development. In addition, significantly larger changes in shape can be attained in one operating step by the wobble-die forging machines in comparison with the multistage dies, necessary for this in conventional extrusion molding, with all their costs and setting-up times.
This wobble-die forging has become increasingly significant, particularly since the required technologies has developed to the extent that functionally capable machines of the afore-named kind are available.
An essential problem remained hitherto unsolved, however, namely, the possibility of the manufacture of precise through bores in the workpiece during its deformation.